Curtain rods which are sold for domestic use fit different sizes of window, door and other openings. Commonly, rods have been adjustable within large and small limits, The present invention relates to curtain rods comprised of round hollow tubes, where one part telescopes within the other part, so the length is adjustable to fit a window or door opening, generally referred to herein as an architectural feature. Many such prior art rods run between opposing side brackets. The brackets may be screwed or nailed to the opposing sides of the frame of the opening. However, for convenience of installation, and to avoid damage to the frame, curtain rods have heretofore been held in place by means of frictional engagement of the rod ends with the opposing sides of a window frame or the like. It follows that there must be means for exerting sufficient force against the window frame surfaces, so the weight of the rod and any associated curtain or other window treatment is supported by frictional engagement; and, that means must be compatible with the need for having adjustable length of the rod.
Another need is that a curtain rod of the foregoing type should be suited for easy installation by an average householder without the use of tools. While there are various designs which are previously known for accomplishing the needs, including those which include tubular rods which have internal springs or mechanical locking mechanisms, there is a continuing need for improved designs which have a better combination of simplicity of installation, good functionality, and economy of manufacture.
In the present invention twisting of one tube relative to the other tube locks the assembly at a particular length. An internal locking mechanism which is connected to the end of the smaller diameter tube expands radially outward and jams against the bore of the larger tube to thereby frictionally lock the tubes to each other. Reversing the direction of the twist loosens the connection. Thus, a curtain rod can be installed at a window opening or frame, to fulfill the needs and functions described above. In known twist lock devices, a sleeve travels along a tapered screw and expands radially outward, for example, as shown in U.S. Pat. No. 5,876,147 of Longo and of U.S. Pat. No. 6,302,614 of Tseng.
Among the problems associated with prior art devices is that the locking sleeve in its relaxed or loosened position does not well-engage frictionally the bore of the larger tube, as is necessary to initiate the tightening process. Another problem is which the present invention seeks to solve is that when a user mistakenly twists the tubes in the loosening direction, the sleeve can become jammed at the small end the tapered screw, causing what is called here false locking. Such wrong-way tightening can even cause the locking mechanism to fracture. A still further problem is that a over-zealous user can over-tighten the locking mechanism, making it difficult to subsequently release.
The foregoing problems can be presented in locking mechanisms used for telescoping tube assemblies for applications other than curtain rods, for instance, adjustable height stands. Thus, there is a need for further improvements in locking mechanism designs that are used with telescoping tube used for curtain rods and other applications.